The NMDA receptor, which is one of glutamate receptors, is located on the nerve cell membranes in the brain and involved in various neurophysiologic events such as neuronal plasticity, cognition, attention, and memory. The NMDA receptor has a plurality of allosteric binding sites, one of which is the glycine binding site (glycine binding site on NMDA receptor complex). It has been reported that the glycine binding site on NMDA receptor complex is involved in the activation of NMDA receptors (Non-Patent Document 1).
Action potential arriving at the presynaptic terminals of glycinergic nerves triggers the release of glycine into synaptic clefts. The released glycine binds to the postsynaptic receptors or the like and is then removed from the synaptic clefts by transporters. Based on this fact, glycine transporters are believed to regulate the functions of NMDA receptors through regulation of the amount of glycine in the extracellular fluid.
Glycine transporters (GlyTs) are proteins involved in the reuptake of extracellular glycine into cells, and two subtypes, GlyT1 and GlyT2, have so far been identified. GlyT1, which is expressed primarily in the cerebral cortex, hippocampus, thalamus and the like, has been reported to be associated with diseases such as schizophrenia, Alzheimer's disease, cognitive impairment, dementia, anxiety disorders (e.g., generalized anxiety disorder, panic disorder, obsessive-compulsive disorder, social anxiety disorder, post-traumatic stress disorder, specific phobias, acute stress disorder), depression, drug dependence, spasm, tremor, pain, Parkinson's disease, attention deficit hyperactivity disorder, bipolar disorder, eating disorder, and sleep disorders (Non-Patent Documents 2-4).
Compounds having a GlyT1-inhibiting action and having an imidazolidin-2-one structure have been reported in the documents shown below (Patent Documents 1 and 2). These compounds described in Patent Documents 1 and 2 are characterized in that a phenyl group is attached via amide or carbonyl to one of the endocyclic nitrogen atoms of the imidazolidine, while another phenyl group is attached to the other endocyclic nitrogen atom of the imidazolidine, and that an endocyclic carbon atom of the imidazolidinone is a spiro carbon atom.